Skateboard riders propel their skateboards, at least on flat or uphill surfaces, by assuming a pushing stance in order to thrust against the ground with one foot while the other foot is positioned on the board. Then, while coasting and maneuvering, a skateboarder places both feet on the board deck in a riding stance, facing sideways relative to the movement of the skateboard, one foot on a front portion of the board and the other foot at the rear. Steering of the skateboard is typically accomplished by the rider leaning laterally with respect to the direction of travel to one side or the other in order to tilt the board. The tilt is converted into a corresponding change of direction of the wheels via front and rear steering trucks. Conventional steering trucks have an axle fixed thereto with wheels mounted for rotation in fixed planes perpendicular to the axle, and employ steering axes diagonally positioned in opposing directions with respect to the vertical (i.e., with the steering axis of one truck angled forwardly and the steering axis of the other truck angled rearwardly) whereby lateral tilting relative to the axles causes the trucks to rotate and steer in the desired direction.
Disadvantages associated with the conventional method of propulsion on flat ground include the fact that additional speed or propulsion is achieved by temporarily leaving the riding stance with two feet on the board to assume the pushing stance with one foot on the board and one foot on the ground. The speeds attainable with such a method are limited. This and other factors have led to efforts at developing pedal-powered skateboards directed toward avoiding the need for alternating between conventional riding and pushing positions.
One prior skateboard as described in U.S. Pat. No. 4,915,403 employs an actuable pedal hinged to the chassis of the skateboard near the middle of the board such that the pedal inclines upwardly from the hinge, the pedal comprising the rear half of the board. During propulsion and riding, one of the rider's feet is positioned on the front portion of the board while the remaining foot presses the actuable pedal downwardly. The motion of pushing the actuable pedal downwardly is transmitted to drive wheels having an overrunning clutch via an elastically mounted push rod used to drive a gear train mounted under the board. The pedal is returned to an elevated position ready for the next stroke by a spring. Though steering of such a board is accomplished according to somewhat conventional diagonal steering axis means, a modified rear truck is required.
Another prior skateboard as set forth in U.S. Pat. No. 4,861,054 uses a pair of actuable pedals, one pedal for each of the rider's feet, wherein each pedal comprises one half of the board surface. The pedals of such skateboard are pivoted to a chassis, and propulsion is accomplished by pushing either or both of the pedals downwardly. Separate push rods for each pedal, drive gears, chain loops and sprockets mounted on shafts in a power transmission train are employed in order to impart rotational motion to a drive wheel. Once the rider's weight has been removed from either or both of the pedals, a spring return system counter-rotates the gears on overrunning clutch bearings to return the pedal or pedals to a ready position. Steering is accomplished by tilting the board from side-to-side, as with conventional boards, but unlike conventional boards the tilting of the board is translated into independent turning of front wheels through a system of steering rods and a rocking pendulum.
An alternative embodiment of the dual pedal propulsion skateboard described in U.S. Pat. No. 4,861,054 employs a relatively wide drive belt running over a system of rollers, the drive belt being fixed near its middle to a center piece of the board and at each end to front and rear drive sleeves that retain one-way clutches for engaging the front and rear wheel axles. Upon depressing, for example, the front pedal, a roller rotatably fixed to the pedal pulls the front portion of the drive belt over other rollers so that the drive belt unwinds from the front drive sleeve causing the front axle to turn drive wheels mounted on the axle. Upon release, the pedal is returned to an elevated position by a spring on the axle whereby the drive belt biases the pedal upwardly as the drive belt rewinds around the drive sleeve. Steering with this embodiment of the dual pedal propulsion skateboard is accomplished in a somewhat conventional manner.
One problem faced by the prior skateboards has been the accommodation of steering or turning and simultaneous propulsion of the wheels by pedal action. That is, there is difficulty in simply and effectively integrating a suitable propulsion system with an advantageous method of steering without producing an unwieldy or expensive board. Preferred conventional steering trucks fixed to the underside of the board have been replaced by complicated, bulky, and perhaps less stable or less efficient steering systems employing special linkages, steering rods, and swinging pendulums, or propulsion systems have been utilized which are difficult to manufacture or which heigthen the profile of the board, leading to instability. Maneuverability has also been a problem.
Another problem, unrecognized by the skateboards described above, is that depression of a single pedal or one of a pair of pedals comprising a rear portion of the board requires the rider to lean in a direction opposite the intended direction of travel of the board in order to supply the weight or force necessary. That is, with such boards, the motion of the rider is in a direction opposite that of the board and very unstable riding conditions can result. Thus, the board tends to "shoot out" from under the rider, especially when first starting to pedal the board.
Still another problem relates to the maximization of propulsion to permit acceleration without unduly elevating the board or inclining the pedal or pedals as would create an awkward or potentially unsafe or unstable riding condition. Attempts to deal with this problem have sometimes resulted in unduly bulky vehicles not closely resembling conventionally popular skateboards. Furthermore, some pedal-propelled skateboards have involved such a departure from conventional skateboards that converting a conventional skateboard to a pedal-propelled skateboard (e.g. with a kit) is not easily accomplished.